diff --git a/intern/cycles/kernel/closure/bsdf_principled_hair_chiang.h b/intern/cycles/kernel/closure/bsdf_principled_hair_chiang.h
index a7bfa8a0320..e31ed134bca 100644
--- a/intern/cycles/kernel/closure/bsdf_principled_hair_chiang.h
+++ b/intern/cycles/kernel/closure/bsdf_principled_hair_chiang.h
@@ -142,11 +142,13 @@ ccl_device_inline float longitudinal_scattering(
   if (v <= 0.1f) {
     float i0 = log_bessel_I0(cos_arg);
     float val = expf(i0 - sin_arg - inv_v + 0.6931f + logf(0.5f * inv_v));
+    kernel_assert(isfinite_safe(val));
     return val;
   }
   else {
     float i0 = bessel_I0(cos_arg);
     float val = (expf(-sin_arg) * i0) / (sinhf(inv_v) * 2.0f * v);
+    kernel_assert(isfinite_safe(val));
     return val;
   }
 }
@@ -185,7 +187,7 @@ ccl_device int bsdf_hair_chiang_setup(ccl_private ShaderData *sd, ccl_private Ch
   kernel_assert(isfinite_safe(bsdf->h));
 
   bsdf->N = Y;
-
+  bsdf->alpha = -bsdf->alpha;
   return SD_BSDF | SD_BSDF_HAS_EVAL | SD_BSDF_HAS_TRANSMISSION;
 }
 
@@ -224,9 +226,9 @@ ccl_device_inline void hair_attenuation(
   Ap_energy[3] *= fac;
 }
 
-/* Given the tilt angle, generate the rotated theta_i for the different bounces. */
-ccl_device_inline void hair_alpha_angles(float sin_theta_i,
-                                         float cos_theta_i,
+/* Update sin_theta_o and cos_theta_o to account for scale tilt for each bounce. */
+ccl_device_inline void hair_alpha_angles(float sin_theta_o,
+                                         float cos_theta_o,
                                          float alpha,
                                          ccl_private float *angles)
 {
@@ -237,12 +239,12 @@ ccl_device_inline void hair_alpha_angles(float sin_theta_i,
   float sin_4alpha = 2.0f * sin_2alpha * cos_2alpha;
   float cos_4alpha = sqr(cos_2alpha) - sqr(sin_2alpha);
 
-  angles[0] = sin_theta_i * cos_2alpha + cos_theta_i * sin_2alpha;
-  angles[1] = fabsf(cos_theta_i * cos_2alpha - sin_theta_i * sin_2alpha);
-  angles[2] = sin_theta_i * cos_1alpha - cos_theta_i * sin_1alpha;
-  angles[3] = fabsf(cos_theta_i * cos_1alpha + sin_theta_i * sin_1alpha);
-  angles[4] = sin_theta_i * cos_4alpha - cos_theta_i * sin_4alpha;
-  angles[5] = fabsf(cos_theta_i * cos_4alpha + sin_theta_i * sin_4alpha);
+  angles[0] = sin_theta_o * cos_2alpha - cos_theta_o * sin_2alpha;
+  angles[1] = fabsf(cos_theta_o * cos_2alpha + sin_theta_o * sin_2alpha);
+  angles[2] = sin_theta_o * cos_1alpha + cos_theta_o * sin_1alpha;
+  angles[3] = fabsf(cos_theta_o * cos_1alpha - sin_theta_o * sin_1alpha);
+  angles[4] = sin_theta_o * cos_4alpha + cos_theta_o * sin_4alpha;
+  angles[5] = fabsf(cos_theta_o * cos_4alpha - sin_theta_o * sin_4alpha);
 }
 
 /* Evaluation function for our shader. */
@@ -293,17 +295,17 @@ ccl_device Spectrum bsdf_hair_chiang_eval(KernelGlobals kg,
   const float phi = phi_i - phi_o;
 
   float angles[6];
-  hair_alpha_angles(sin_theta_i, cos_theta_i, bsdf->alpha, angles);
+  hair_alpha_angles(sin_theta_o, cos_theta_o, bsdf->alpha, angles);
 
   Spectrum F = zero_spectrum();
   float F_energy = 0.0f;
 
   /* Primary specular (R), Transmission (TT) and Secondary Specular (TRT). */
   for (int i = 0; i < 3; i++) {
-    const float Mp = longitudinal_scattering(angles[2 * i],
+    const float Mp = longitudinal_scattering(sin_theta_i,
+                                             cos_theta_i,
+                                             angles[2 * i],
                                              angles[2 * i + 1],
-                                             sin_theta_o,
-                                             cos_theta_o,
                                              (i == 0) ? bsdf->m0_roughness :
                                              (i == 1) ? 0.25f * bsdf->v :
                                                         4.0f * bsdf->v);
@@ -347,6 +349,7 @@ ccl_device int bsdf_hair_chiang_sample(KernelGlobals kg,
   kernel_assert(fabsf(dot(X, Y)) < 1e-3f);
   const float3 Z = safe_normalize(cross(X, Y));
 
+  /* wo in pbrt. */
   const float3 local_O = make_float3(dot(sd->wi, X), dot(sd->wi, Y), dot(sd->wi, Z));
 
   const float sin_theta_o = local_O.x;
@@ -387,19 +390,20 @@ ccl_device int bsdf_hair_chiang_sample(KernelGlobals kg,
     v *= 4.0f;
   }
 
+  float angles[6];
+  hair_alpha_angles(sin_theta_o, cos_theta_o, bsdf->alpha, angles);
+  float sin_theta_o_tilted = sin_theta_o;
+  float cos_theta_o_tilted = cos_theta_o;
+  if (p < 3) {
+    sin_theta_o_tilted = angles[2 * p];
+    cos_theta_o_tilted = angles[2 * p + 1];
+  }
   rand.z = max(rand.z, 1e-5f);
   const float fac = 1.0f + v * logf(rand.z + (1.0f - rand.z) * expf(-2.0f / v));
-  float sin_theta_i = -fac * sin_theta_o +
-                      cos_from_sin(fac) * cosf(M_2PI_F * rand.y) * cos_theta_o;
+  float sin_theta_i = -fac * sin_theta_o_tilted +
+                      sin_from_cos(fac) * cosf(M_2PI_F * rand.y) * cos_theta_o_tilted;
   float cos_theta_i = cos_from_sin(sin_theta_i);
 
-  float angles[6];
-  if (p < 3) {
-    hair_alpha_angles(sin_theta_i, cos_theta_i, -bsdf->alpha, angles);
-    sin_theta_i = angles[2 * p];
-    cos_theta_i = angles[2 * p + 1];
-  }
-
   float phi;
   if (p < 3) {
     phi = delta_phi(p, gamma_o, gamma_t) + sample_trimmed_logistic(rand.x, bsdf->s);
@@ -409,17 +413,15 @@ ccl_device int bsdf_hair_chiang_sample(KernelGlobals kg,
   }
   const float phi_i = phi_o + phi;
 
-  hair_alpha_angles(sin_theta_i, cos_theta_i, bsdf->alpha, angles);
-
   Spectrum F = zero_spectrum();
   float F_energy = 0.0f;
 
   /* Primary specular (R), Transmission (TT) and Secondary Specular (TRT). */
   for (int i = 0; i < 3; i++) {
-    const float Mp = longitudinal_scattering(angles[2 * i],
+    const float Mp = longitudinal_scattering(sin_theta_i,
+                                             cos_theta_i,
+                                             angles[2 * i],
                                              angles[2 * i + 1],
-                                             sin_theta_o,
-                                             cos_theta_o,
                                              (i == 0) ? bsdf->m0_roughness :
                                              (i == 1) ? 0.25f * bsdf->v :
                                                         4.0f * bsdf->v);
diff --git a/tests/data b/tests/data
index 9c778e46424..753727081d7 160000
--- a/tests/data
+++ b/tests/data
@@ -1 +1 @@
-Subproject commit 9c778e4642436b603d51923213483cccef1d08a1
+Subproject commit 753727081d73e1469f45fb9b36ad081c12cfcfab